Tensioning device for printing presses



May 9, 1961 c. E. FULLER TENSIONING DEVICE FOR PRINTING PRESSES FiledMarch 27, 1959 POLARIZED RELAY PHASE POLARIZED DEMODULATOR A:

COMPUTER INVENTOR. CHARLES E. F LLEQ ATTORNEYS United States. PatentDPatented May 9,1961;

This invention relates generally to tension control of an elastic orsemi-elastic strip being drawn oif a roll and into a printing machine tobe printed, and more particular-- ly concerns apparatus for finely orclosely controlling the strip tension so that printed impressions willbe'very accurately located on the strip.

Among the problems solved by the use of the present control apparatus isthe commonly experienced lack of sufiicient accuracy in locating printedimpressions on paper or plastic such as cellophane strip material beingsupplied to a rotary press ofi a supply roll. For example,

if the tension of the feed strip is not held very nearly constant, it isnot possible to superimpose on the strip different colored impressionswith sufiicient accuracy, as by means of a rotary press, to preventready discernment of errors in color superposition along portions of thestrip supplied off the roll. At the present time, it is the practice inthe rotary press printing art to manually control or adjust the tensionin the feed strip being rapidly unrolled and fed to the rotary press, asby watching an idler roller engaging the strip and adjusting a brakingdevice acting on the supply roll when the idler.

roll deflects. Such idler rollers commonly undergo deflections as muchas four inches, showing that the brake operator cannot manually veryclosely control the strip tension. Particularly is this true when theroll is nearing the end of unwinding, inasmuch as its angular velocityis then approaching a maximum as its mass approaches a minimum, makingclose control of braking extremely diflicult. As a result, gross errorsin registry of successively superimposed printing impressions,particularly in difierent colors, clearly appear, and it is not uncommonto reject upwards of of the total printed strip or paper as being sobadly out of multicolored print registry as to be unusable. Also,discrepancies in winding of the strip on the roll cause loosenesscontributing to undesired tension of the feed strip and lack of correctmulticolor registry.

Accordingly, it is a major object of the present invention to overcomethe discussed problem of obtaining satisfactory registration ofmulticolored print, through the use of the novel control apparatus to bedescribed in detail. As broadly conceived, that apparatus is operable tofinely control feed strip tension and comprises follower meansengageable with the feed strip to be moved in response to small changesin strip tension, control means operable to produce a magnetic fieldfor. producing force actuable to brake rotation of the supply roll andthereby to resist drawing of the strip oil the roll, together withelectrical circuit means cooperative with the follower and control meansto vary the magnetic field in response to movement of the followermeans. As a result braking of the feed roll is respectively'increasedand decreased in response to slight decreases and increases of striptension relative to a predetermined value of such tension. In fact, asslight a deflection of the follower means as of an inch is sufiicient toalter almost instantaneously the magnetic field produced by the controlmeans so as to effect achange in the braking force acting on the feedroll to restore the desired strip tension.

While the invention contemplates various ways in which braking force canbe applied or transmitted to the feed roll in response to changes in themagnetic field produced 'by the control means, it is directedparticularly to the use of a rotary type electrical machine such as abi-directional motor, for producing the magnetic field from which torqueis transferrable to brake the feed roll. Also, the invention ischaracterized in that the electrical circuit operable to vary themagnetic field produced bythe electricalmachine includes an electricalbalance type bridge, the output of which is adapted to change inresponse to slight oppositely directed movements of the follower means.

Other objects and advantages of the invention include the use of meansfor converting the bridge output into either phase or polarity polarizedcontrol signals which are operable through a relay to controldirectional magnetization of the electrical machine or bi-directionalmotor, so as to drive a rotary part of the motor in opposite directions.Such opposite directional drive is then transmissible to a braking nuton the screw of a roll brakinvention, aswell as the details of anillustrative embodiment, will be more fully understood from thefollowing detailed description of the drawings, in which:

Fig. l is a schematic showing of the control apparatus .as applied to aprinting press;

Fig. 2 illustrates the apparatus for sensing changes in strip tension;and

Fig. 3 shows the releasable drive connection between the bi-directionalmotor and braking nut operable to control braking of the feed roll.

In Fig. 1 the elements of a printing press that are shown include thesupply roll 10 oil which a strip 11 of paper or the like is drawn undera guide roller 12, and between pinch rollers 13 for subsequent travelthrough multi-color printing rollers not shown.

Conventionally incorporated with the feed roll is a braking device 14shown in outline in Fig. 3, and which acts to variably brake the rollinaccordance with the position of a braking nut 15 on a screw 16 so thatthe paper or strip 11 remains under tension as it is drawn through thepress. Turning of the control nut 15 in a clockwise direction effectsincreased braking of the feed roll while turning of the nut in acounter-clockwise direction as viewed from the projecting end of thescrew 16' decreases the braking effect. In accordance with theinvention, increased braking.

effort causes the tension in the feed strip 11 to increase, such tensionchange being sensed by a follower roller 17 seen in Figs. 1 and 2 and inengagement with the side of the strip. The roller is mounted on an axle18 carried by a body 19 which is spring loaded in opposite directions bythe compression springs 20. The spring loading is adjustable tocorrespond to any desired tension in the feed strip 11, and accordinglyshould the tension increase above this level, the roller 17 will bedeflected downwardly; whereas should the tension decrease below thedesired level the follower roller 17 will rise against the strip 11 in adirection normal to the strip travel.

arm or lever 21 which is attached to the body by means Upand downmovement of the body 19 is transmitted toan.

of a pin 22 projecting through a slot 23' in' the arm, the

pinbeing carried by the body. The lever is fulcrumed by a pin 24carrying a wiper arm shown schematically at 25 in Fig. l, the wiperbeing pivoted about the axis of pin 24 as. the body 19 moves up anddown. The wiper arm 25 is apart of the potentiometer generally shown at.26 in Fig. 2. as. being circular in form and being mounted or fixed on.structure 27 relative to which the body 19 moves up anddown.

The resistance slide wire 28 of the potentiometer 26 has its endterminals connected with the end terminals of a coil 29 which forms thesecondary of an iron core transformer 30, the primary winding of whichis indicated at 31. Thus, the resistance 28 and secondary coil 29 areconnected in parallel to form a bridge circuit characterized in that thecenter tap 32 of the coil 29 is grounded.

' The. voltage output of the bridge circuit is fed through the wiper arm25 of the potentiometer 26 and drops through a resistor 33 grounded at34, the resistor being adjustably tapped at 35 so as to vary the outputfed to the amplifier 36. effects control of the tension of the strip 11in a very simple manner.

The amplified output of the bridge circuit is then fed at 37 to ademodulator and computer indicated generally at. 38 operable to convertthe bridge output into polarized control signals corresponding to slightdeflections of strip tension greater and lesser than desired tension. Areference signal is also fed through leads 39 to the demodulator andcomputer 38, the reference signal having been obtained from thesecondary winding 40 which is center tapped and grounded as indicated at41.

The demodulator and computer is shown in block form since various knowncircuits can be used for demodulating the bridge output through the useof a reference signal as indicated and polarizing the output to producepolarized control signals fed at 42 to a polarized control relay 43 alsoindicated schematically. The control signals fed to the relay in turngovern relay operation to control power input fed at 44 to abi-directional control motor 45, the

power input to the relay being shown at 146. The direction of rotationof the motor and its reaction speed are determined or controlled, forA.C. applications, by the phase polarity and amplitude of the controlsignal, whereas for D0. applications the direction and reaction speed ofthe motor are controlled by the positive and negative polarity andamplitude of the control signals.

It is emphasized that through the provision of the amplifier 36 verysmall. changes in strip tension giving rise to small bridge outputs aresensed and immediately converted to control signals operable to controlthe direction of rotation and torque of the motor 45 throughthe controlof the magnetic field produced in the motor as a result of' relayoperation. Changes in torque or force is then transferable to brake thesupply roll and thereby increase or decrease resistance to drawing ofthe feed strip off the roll, all for the purpose of restoring thedesired tension in strip 11. As an illustration of the control of themagnetic field produced in the motor, the power input to one or more ofthe windings of the motor may be controlled by the relay 43 so as toeffect the desired direction of motor rotation and the torque producedto accomplish the desired braking effect.

- Turning again to Fig. 3, the motor 45 has an output shaft 46 which isslotted at 47 in an axial direction, and to a depth considerably lessthan the diameter of the shaft. Projecting into the slot 47 is theterminal end of a set screw 43 received in a flange 49 mounted on theshaft 46 to slide axially thereon. The set screw 48 is tightenable by aknurled nut 50 so as to locate or fix the flange 49 on the shaft 46 inany desired axial position thereon.

Attached to the flange 4? are two or more studs 51 extending in parallelrelation with'respect to the axis of the shaft 46, the ends of the studs51 being slidably received As will appear, adjustment of the tap 35-essence within corresponding openings 52 such as are formed by bronzesleeves 53 affixed within the braking nut 15. Thus, as the flange 49 isturned by the shaft 46 in a direction so as to tighten the braking nut15 to increase the braking effect transmitted by the braking device 14to the supply roll 10, the nut 15 will move axially relatively away fromthe studs 51. The terminal ends 55 of the studs are so positioned withinthe nut 15 that the studs 51 completely disengage the nut in the eventthat the nut is tightened to increase the braking exertion on the rollto such an extent that further tightening of the nut 15 would overloadthe motor 45. The motor rotor and stator parts by means of which themagnetic field is. produced, are shown at 60 and 61.

The drawings are to be regarded merely as illustrative of the invention,and it will be understood that various changes and additions may be madewithout departure from the invention in its intended spirit and scope.

I claim:

1. For combination with a printing machine operable to draw a printablestrip of material off a supply roll to be printed in the machine, andfollower means engageable with a side of the feed strip to be movedthereby in opposite directions substantially normal to strip travel inresponse to small changes in strip tension, the improvement whichcomprises control means including a rotary type electrical machine forproducing a magnetic field from which torque is transferrable to brakethe supply roll and thereby to resist drawing of the strip oflf saidroll, and an electrical circuit controllable. by said follower means andelectrically connected with said electrical machine, said circuit beingoperable to vary said magnetic field in response to movement of saidfollower means, whereby braking of the supply roll. is respectivelyincreased and decreased in response to small decreases and increases ofstrip tension relative to a predetermined value thereof, said circuitincluding an electrical balance type bridge the output of which isadapted to change in response to slight oppositely directed movements ofsaid follower means, said circuit including computer means forconverting said bridge output into polarized control signalscorresponding to slight deviations in strip tension greater and lesserthan desired tension, said signals being operable to control saidmagnetic field for increasing and decreasing said torque, and means forproducing a reference signal to be compared in the computer means withsaid bridge output.

2. The invention as defined in claim 1 in which said circuit meansincludes an amplifier electrically connected between said bridge andcomputer for amplifying said bridge output to be converted in thecomputer.

3. T he invention as defined in claim 1 including means for transmittingbraking torque operable to effect braking of said roll, and in whichsaid electrical machine comprises a motor having a rotary part connectedwith said braking torque transmitting means and adapted to be driven inopposite rotary directions in response to production of said controlsignals.

4. The invention as defined in claim 3 in which said circuit includes arelay through which said control signals are operable to control powerinput to-said motor so as to drive said rotary part in oppositedirections.

5. The invention as defined in claim 3 including a roll braking devicehaving a screw, and in which said. means for transmitting braking torqueincludes a braking nut adapted to be driven by said motor on the screwof said roll braking device.

6. The invention as defined in claim 5 in which said means fortransmitting braking torque includes a drive connection between themotor and nut, said connection being releasable to permit manualmanipulation of the braking nut.

7. The invention as defined'in claim 6 in which the nut is movable onthe screw relative to the drive connection and out of driven relationtherewith as the nut operates 5 to increase braking of the feed roll,whereby overloading References Cited in the file of this patent of themotor is prevented.

8. The invention as defined in claim 1 in which said UNITED STATEDPATENTS bridge includes a potentiometer and in which said fol- 1,103,153Morse July 14, 1914 lower means is connectible to the movable part ofsaid 5 1,286,331 James Dec. 3, 1918 potentiometer the movement of whichaffects the bridge 1,852,575 Howe Apr. 5, 1932 1 1,896,209 Vitale et a1Feb. 7, 1933 output.

